Circuit arrangement for indicating electric field strength

Abstract

An FM receiver capable of generating a signal showing the electric field intensity of a received signal. More particularly, an FM receiver capable of generating a signal showing the electric field, wherein the dynamic range is expanded, and the linearity is improved. The enlargement of the dynamic range of the signal showing the electric field intensity may be effected, and also the linearity may be improved. Accordingly, the electric field intensity of the received signal may be correctly displayed by a display, etc. Especially, as the gain control is effected through the control of the operation current of the gain control amplification circuit in accordance with the gain control signal by the differential type of level detection circuit, an FM receiver suitable for IC may be provided.

What is claimed is: 
     
       1. A circuit arrangement for indicating an electric field strength of a high frequency FM signal received in an FM receiver that has means for receiving the high frequency FM signal and for providing an intermediate frequency (IF) signal, multistage IF limiting amplification circuit means responsive to said receiving and providing means for amplitude limit amplifying of said IF signal so as to produce output signals which are limited in amplitude, and means responsive to said multistage IF limiting amplification circuit means for detecting said output signals, the circuit arrangement comprising: amplifying means for amplifying said IF signal to produce an amplified output signal, said amplifying means being connected to a signal path between said receiving and providing means and said multistage IF limiting amplification circuit means so that said IF signal being amplified by said amplifying means is free from being limited in amplitude by said multistage IF limiting amplification circuit means;   level detecting means responsive to said amplifying means for level detecting said amplified output signal to produce a level detected output signal; and   generating means for generating a control signal in accordance with said level detected output signal, said amplifying means having a gain and being responsive to said generating means so that said gain varies in accordance with said control signal and so that as an electric field strength of the high frequency FM signal received increases, said gain decreases so as to thereby enlarge a dynamic range for indicating said electric field strength of the high frequency FM signal received.   
     
     
       2. A circuit arrangement as in claim 1, wherein said generating means generates said control signal for reducing said gain of said amplifying means as said electric field strength of the high frequency FM signal received increases. 
     
     
       3. A circuit arrangement as in claim 1, wherein said level detecting means includes first and second transistors each having an emitter and collector, means for connecting each of said emitters to each other, current mirror circuit means for producing output current, means for connecting each of said collectors to said current mirror circuit means, and means for smoothing said output current from said current mirror circuit means so as to generate signals indicative of said electric field strength. 
     
     
       4. A circuit arrangement as in claim 1, wherein said amplifying means is responsive to said control signal such that said gain varies in response to a variance in said electric field strength. 
     
     
       5. A circuit arrangement for indicating electric field strength, comprising: gain control amplification means for amplifying output signals;   level detection means for level detecting the output signals, said level detection means comprising first and second transistors differentially connected to each other and each having one collector generating collector current, and current mirror circuit means for producing output current and receiving said collector current from said one collector of said first and second transistors as input; and   means for smoothing said output current so as to produce output signals indicative of electric field strength.   
     
     
       6. A circuit arrangement as in claim 5, further comprising: means for controlling gain in accordance with said output signals indicative of electric field strength.